In the related art, a printing method, which uses an ink jet recording method, discharges and causes small ink droplets to fly from a print head, and attaches the ink droplets onto a recording medium, such as a paper sheet. At a time of discharging ink, a discharging failure tends to occur due to bubbles generated in the ink. Here, various technologies, which eliminate the bubbles and stably discharge the ink droplets by using a deaerator or the like and deaerating the ink, have been suggested.
For example, JP-A-2011-42104 discloses deaerated ink (air decompression rate of a film deaeration module is −90 kPA, and dissolved oxygen of the ink at a module outlet is 1.86 ppm (20° C.)) which is made by deaerating cyan ink made of 13 mass % of reactive and water-soluble dye (C. I Reactive Blue 72), 60 mass % of ion exchanged water, 23.7 mass % of ethylene glycol, 0.3 mass % of surfactant (Olefin E 1010:acetylenic glycol-based surfactant manufactured by Nissin Chemical Industry Co., Ltd.), and 2 mass % of anti-mold agent (Proxel GXL-S manufactured by Arch Chemicals Co., Ltd.), by using a film deaeration module (external refluxing type, EF-G3 manufactured by DIC Co., Ltd) (refer to paragraphs 0120 and 0124 in JP-A-2011-42104).
In addition, for example, as an ink supply method to the print head, a method of supplying the ink to the print head which is attached to a printer via a tube from an ink outlet portion of an ink tank, is disclosed (for example, JP-A-2011-4210 and JP-T-11-504874). According to the ink supply method disclosed in JP-A-2011-42104 and JP-T-11-504874, the ink tank is provided with a liquid pouring path (hereinafter, referred to as an “ink filling port”, or a “liquid pouring portion”), and a user can easily pour the ink from the liquid pouring path.